1. Field of the Invention
The present invention relates generally to magnetic position sensors, and, more particularly, to a magnetic position sensor which utilizes two generally parallel target tracks in conjunction with two magnetically sensitive components arranged with a biasing magnet.
2. Description of the Prior Art
Many different types of magnetic position sensors are known to those skilled in the art. In one particular adaptation of a magnetic position sensor, one or more magnetically sensitive devices, such as Hall effect components, are arranged proximate a moving target of magnetic material and a permanent magnet is used to provide a biasing magnetic field which is distorted in response to movement of magnetic material through the field. This type of configuration is commonly used in association with geartooth sensors, wherein a Hall effect element is disposed proximate the teeth of a moving gear with a permanent magnet disposed proximate the Hall effect element to provide a magnetic field which passes through the Hall effect element and the teeth of the gear. As the gear rotates, successive teeth and interstitial gaps move past the Hall effect element. Typically, the Hall effect element is disposed between the gear and the source of the magnetic field, such as a permanent magnet. As the gear teeth pass through the magnetic field, the field is distorted and the direction and strength of the field passing perpendicularly through the Hall effect elements is caused to change in response to the moving gear teeth. Since Hall effect elements commonly provide an output signal that is representative of the magnetic field strength perpendicular to the Hall effect element, the output signal can then be interrogated to determine the presence of gearteeth or interstitial gaps at a particular position relative to the Hall effect element.
U.S. Pat. No. 5,140,262, which issued to Stolfus on Aug. 18, 1992, describes a geartooth sensor with a centerline in nonintersecting relation with a center of rotation of a rotatable member. The off axis geartooth sensor is provided with a centerline of the sensor disposed along a line which is not coincident with the center of rotation of the rotatable member to be sensed. Instead, the centerline of the housing in which a Hall effect element is disposed is pointed at a perpendicular distance from the center of rotation of the rotatable member which is determined as the function of a range of dimensions which define the allowable gap between the Hall effect element and a surface of the rotatable member.
U.S. patent application Ser. No. 07/865,010 (M10-14049) which was filed on Apr. 8, 1992, now U.S. Pat. No. 5,304,926, by Wu and assigned to the assignee of the present application, discloses a position sensor which is provided with two magnetically sensitive devices associated with a magnet. The sensor is disposable proximate a rotatable member having at least one discontinuity in its surface. The two magnetically sensitive devices, which can be Hall effect transducers, each provide output signals that represent the direction and magnitude of the magnetic field in which its respective transducer is disposed. An algebraic sum of the first and second output signals from the magnetically sensitive devices is provided as an indication of the location of the rotatable member that is disposed proximate the sensor.
U.S. patent application Ser. No. 07/952,449 (M10-15101), which was filed by Wu on Sep. 29, 1992, now U.S. Pat. No. 5,341,097, discloses a geartooth sensor which incorporates a magnet and two magnetically sensitive devices, such as Hall effect elements. The two magnetically sensitive devices are disposed in a common plane with each other with one of the devices being located at a position closer to the magnet than the other device. The common plane in which both magnetically sensitive devices are disposed is faced apart from a central axis of the magnet by a predetermined distance. A means is provided for determining a ratio of the magnetic field strengths that are imposed perpendicularly on the first and second magnetically sensitive devices. The ratio is used to distinguish between teeth and slots proximate the sensor, wherein the common plane of the magnetically sensitive devices is generally perpendicular to the path along which the teeth and slots pass.
U.S. Pat. No. 5,164,668, which issued to Alfors on Nov. 17, 1992, describes an angular position sensor with decreased sensitivity to shaft position variability. The angular position sensor is provided with first and second pole pieces that extend from regions proximate a rotatable magnet to regions proximate a magnetically sensitive device. The pole pieces provide defined magnetic paths of lowered reluctance that confine the lines of flux extending between the rotatable magnet and the magnetically sensitive device. The placement of the rotatable magnet between first and second pole piece segments of the invention significantly reduces the sensitivity of the sensor to variations in possession of the rotatable magnet and therefore increases the reliability of the measurement system.
U.S. Pat. No. 5,159,268, which issued to Wu on Oct. 17, 1992, describes a rotational position sensor with a Hall effect device and a shaped magnet. A Hall effect device is provided for use as a rotary position sensor in cooperation with a shaped magnet that imposes a magnetic field on the Hall effect device which is generally linear and proportional to the angular position of the shaped magnet. Two alternative embodiments are described and illustrated which both provide a high degree of linearity between the electrical output of the Hall effect device and the rotational position of the shaped magnet. One of the alternative embodiments is generally oblong and the other alternative embodiment is generally bell shaped. Both of these alternative embodiments exhibit a high degree of linearity between the strength of the magnetic field imposed on a Hall effect element and the rotational, or angular, position of the angular magnet.
In applications of the type described above, the strength of the magnetic field perpendicular to the Hall effect element is caused to change from one positive magnitude of a magnetic field to a greater or slightly lesser positive magnitude of magnetic field. The change in magnetic field strength causes a measurable change in the output of the Hall effect component. This change in output signal can be used to determine whether a tooth or a gap is proximate the sensor.
Certain applications of sensors of this general type incorporate moving targets which comprise unequal spaced and sized teeth or magnetic segments. The use of unequal magnetic segments permits the moveable target device to provide a code which permits the system to more accurately determine the position of the target. For example, if certain teeth or segments are larger than others, the smaller and larger segments can be arranged in a predefined pattern to permit the device to more accurately determine the position of the target without requiring a complete cycle of the teeth or segments.